Step 5: Testing and Rewireing

Step 6: Video of Finished Project

In the below video you can see the finished robot running forward. I hope you enjoyed this Instructable! Any comments or constructive criticism is ve...

Update; My age category for the contest is 13-18 because I am fifteen. :)

Yes, the title explains it pretty well. In this Instructable I will show you step by step how to construct a light sensitive, solar powered, robot. All you need is some parts that can easily be found in the trash or in your backyard. I built mine totally from trash.

Step 2: And so it begins...

Begin with the old solar light, you will have to open up the top and remove the solar panel and control circuit without damaging any of it. Follow the notes on the pictures to see how. Make sure to read all the notes as some wires need to be cut, while others do not.

Are you from outside the United States? They are very popular here within the urban communities. I don't know about Europe, but you can find them at almost every garden section in any store in the U.S.

If you really want to win a science fair, I suggest you build my version 2. Which is obstacle avoiding. I have no instructable, but I would be willing to send you pictures and instructions if you would like. :-)

IF you happened to have a rc car that drove with a differential (0 degree) drive, you MIGHT be able to jerry-rig the circuit to control the two motors... :-/ Although it seems to me like a waste of a rc car and time. Unless your overall purpose was to create a rc robot shaped like a bug.If you have something specific in mind let me know and I'll see if I can help.

Actually, if you had two identical circuits from solar lights, you could just put one motor for each circuit, (or two on a tank!), and criss-cross the light sensors and have yourself a solar powered light seeking robot.

martzsam, Cool project, but I don't quite understand what is going on.

Do the batteries need to be charged to get the 'nominal' motion and the extra light on the cell adds the additional power to increase its speed? Said another way, without the batteries does the robot move in the light but only at 1/2 speed?

Or is the extra light only hitting the light sensor and that's what's increasing the speed of the bot? (This wouldn't make sense because the light sensor is supposed to turn off the device when it gets too light)

Did you have to do something to the light sensor since normally the light sensor turn off the power to the circuit when it is sensing light since this function is to turn on the 'load' when it gets dark? Said another way does the robot stop moving in bright light?

Are the batteries wired in parallel or serial? If serial then I wouldn't think that they were being charged at all since the circuit would be designed to charge a single cell and would not provide sufficient voltage to charge two cells.

It would be nice if the robot would continue to charge the battreries when switched off. Have you cheked that there is no current going to the betteries when the switch is in the off position? Without knowing the circuit design we really aren't sure what's going on in it, like it operation in the off position, how the light sensor works, or if the battery charging circuit has over charging protection.

1. The robot doesn't work without the batteries, I worked it so the robot starts with a full charge, then maintains that charge with the panel while it is running. The solar panel does not directly power the motors. It like just adding on another battery that never dies in parallel.

2. The batteries are wired so their gross output is only 1.2 volts, not 2.4. This allows for the 3 volt soar panel to do its job charging them even in low light. In other words, yes they are wired in parallel. (which is probably important and I should update that...)

3. There is absolutely no current going to the batteries when the switch is off because the switch is right on the positive out from the pack.

4. And when you said,

"Or is the extra light only hitting the light sensor and that's what's increasing the speed of the bot? (This wouldn't make sense because the light sensor is supposed to turn off the device when it gets too light)"

you are totally correct, because the panel doesn't power the motors directly, the circuit relies on the light sensor to tell it when to speed up or slow down.

Can you explain why the light sensor speeds up the motors? Do the motors simply replace each LED (and one motor explicitly does so, if I read it right, I guess the other one to)? One would expect the motors to slow down when the light hits the sensor. Or am I missing some alterations to the to the garden light's circuit?

A garden light' s circuit normally contains some kind of joule thief circuit to drive the LED(s) from a single 1.2 V battery, with an extra to have darkness switch it on.Maybe the light sensor influences the balance between voltage and current? When dark: high voltage, low current needed for a LED, when light: low voltage, LED doesn't work, but higher current possible.LEDs cut off below a certain voltage, no matter the current, while motors are strongly controlled by current. Of course motors are at the same time controlled by voltage, but I expect the garden light circuit to provide a rather low current (designed for LEDS), making this current the limiting factor.

I did replace the LED's with the motors, and I think that the circuit works the way it does because LED's also act like resistors, and when replaced with a motor that has a different resistance, it alters the circuits function. Its like taking a circuit and replacing the resistors with weaker resistors. I don't exactly know how the light sensor influences this.